Dual spring flow control valve

ABSTRACT

An electropneumatic proportional flow control device improves electropneumatic control of pneumatically operated valves. Improved turn down ratios in regards to the electromagnetic response of the device to a supplied control voltage is achieved using two variable spring devices, one linear, as part of the pressure regulator valve component, and the other non-linear, as part of the proportional valve component and which are magnetically responsive to different magnetic forces. The use of both the linear and non-linear springs together results in an increased turndown-ratio, especially during initial valve control.

FIELD OF THE INVENTION

The present invention relates generally to a device for electromagneticcontrol of pneumatically operated valves and, more specifically to sucha valve having an armature design and method of operation such as toallow improved turndown ratios.

BACKGROUND OF THE INVENTION

Numerous types of proportional pneumatic flow control valves arepresently available which accurately control flow over a wide range offlow control applications. However, a problem with current flow controlvalves is that they generally do not offer precision flow at lowerrates. For balanced valves the valve percentage of error for the fullscale of the valve may be too great; and, the low flow imprecision canbe too problematic to the application. As such, to control such a systemwith PID controllers to eliminate such wide swings that are inherentwithin the system remains very difficult.

Unbalanced valves are (usually) simpler designed, smaller valves withlow pressure drops across the valve. Advantages include a simpler designwith fewer potential leak paths at the seat and a lower capital cost.Disadvantages include a limited sizes, since with a large unbalancedvalve the forces needed to seat and hold the flow often becomesimpractical. A general solution is to maintain holes through the plug inorder to achieve an easier shut off as the plug does not have toovercome static forces. However, such a solution creates an additionalleak path and at a cost that is generally higher.

In trim control applications, the selection of balanced or unbalanceddesigns is not entirely straightforward, and will ultimate be based uponthe selection and design of the actuator. The actuator design is basedon the thrust force which is required to open and close the valve, withthe returning forced being supplied by either a spring or diaphragm.Selection of an actuator and spring range must be capable of handlingthat thrust force which is available in the selected size of valve.

To date the only conventional way to proportionally control the flowrate of a medium with flow control valves over wide swings in flow andpressure is to use two separate mechanical valves in sequence. Using twoindependent valves in parallel or in series will increase accuracy overparticular segments of the full flow range. One valve is typically usedfor lower flow rates, and then a larger valve subsequently compensatesfor the higher flow rates. Both valves are independently controlled.

Consequently, there is a need for a single balanced valve mechanism thatallows for an increase in the precision of low flow output during theinitial flow performance of a device's full-scale flow capability whilealso allowing for higher volume flow for a remaining portion of thefull-scale output.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved deviceand method for the electropneumatic control of pneumatically operatedvalves.

It is a feature of the present invention to provide a valve having anarmature design and method of operation such as to allow improvedturndown ratios.

Briefly described according to the present invention, a uniqueelectropneumatic proportional flow control device and method that allowsfor improved valve actuation and an improved turn down ratio in regardsto the electromagnetic response of the device to a supplied controlvoltage. This is achieved using two variable spring devices, one linearand the other non-linear, which are magnetically responsive to differentmagnetic forces. The linear spring improves the valve actuation; thevalve actuation being precision control over the initial “lift offcurrent”, which is the current required to initiate flow through thevalve, thereby overcoming the preloaded spring force which seals theinner valve to the valve seat. By using a linear spring, which isresponsive to the relatively lower beginning magnetic pull of the valvecoil, there is less variation in setting the initial preload force ifthe spring. The non-linear spring is utilized for the relatively highermagnetic pull of the valve coil for improved control over the greatermagnetic force required for higher flow rates. The spring forceresistances is non-linearly related to the magnetic actuation force.

The use of both the linear and non-linear springs together results in anincreased turndown-ratio, especially during initial valve control.

Further advantages include a control mechanism that is small,lightweight, and insensitive to position or vibration. Such a device canbe readily mounted in a process line to be controlled at its work point,with valves incorporating the present teachings being very well adaptedfor use as a main flow control valve for various medical products.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages and features of the present invention are better understoodwith reference to the following and more detailed description and claimstaken in conjunction with accompanying drawings, in which like elementsare identified with like symbols:

FIG. 1 is a side elevation view of a dual mode electropneumatic flowcontrol valve according to the present invention, wherein electroniccircuitry is shown in block-form; and

FIG. 2 is a cross sectional view taken along line II-II if FIG. 1;

FIG. 3 is a perspective view of a nonlinear flat coil spring 12 for usein conjunction with the flow control valve according to the presentinvention for use in the relatively higher magnetic pull of the valvecoil for improved control over the greater magnetic force required forhigher flow rates; and

FIG. 4 is a perspective view of a linear flat coil spring 11 for use inconjunction with the flow control valve according to the presentinvention for use in a predictable preloaded travel at the valve openingfor precision control over the initial “lift off current”, which is thecurrent required to initiate flow through the valve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The best mode for carrying out the invention is presented in terms ofits preferred embodiment, herein depicted within the Figures. Furtherfor purposes of the present application and for convenience, certainterms employed in the specification, examples, and appended claims arecollected here. Unless defined otherwise, all technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e., to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

The terms “comprise,” “comprising,” “include,” “including,” “have,” and“having” are used in the inclusive, open sense, meaning that additionalelements may be included. The terms “such as”, “e.g.”, as used hereinare non-limiting and are for illustrative purposes only. “Including” and“including but not limited to” are used interchangeably.

The term “or” as used herein should be understood to mean “and/or”,unless the context clearly indicates otherwise.

To promote an understanding of the principles of the present invention,the embodiment is hereafter explained with reference to respectivedrawings as well as to specific language to describe the same.

The term “actuator” should be understood broadly as being any pneumatic,hydraulic, or electrically powered device which supplies force andmotion to open or close a valve.

The term “air set” as used herein should be understood to mean aregulator which is used to control the supply pressure to the valveactuator and its auxiliaries.

The term “bench set” as used herein should be understood to mean thecalibration of the actuator spring range of a control valve, to accountfor the in service process forces.

The term “body” as used herein should be understood to mean the mainpressure boundary of the valve that also provides the pipe connectingends, the fluid flow passageway, and supports the seating surfaces andthe valve closure member.

The term “bonnet” as used herein should be understood to mean theportion of the valve that contains the packing box and stem seal and mayguide the stem. It may also provide the principal opening to the bodycavity for assembly of internal parts or be an integral part of thevalve body. It may also provide for the attachment of the actuator tothe valve body. Typical bonnets are bolted, threaded, welded to,pressure-sealed, or integral with the body.

The term “cage” as used herein should be understood to mean the part ofa valve trim that surrounds the closure member and may provide flowcharacterization and/or a seating surface. It may also providestability, guiding, balance, and alignment, and facilitate assembly ofother parts of the valve trim.

The term “capacity” as used herein should be understood to mean the rateof flow through a valve under stated conditions.

The term “cavitation” as used herein should be understood to meantwo-stage phenomenon of liquid flow. The first stage is the formation ofvapor bubbles within liquid system due to static pressure of fluid atvena contracta falling below the fluid vapor pressure: the second stageis the collapse or implosion of these cavities back into an all-liquidstate as the fluid decelerates and static pressure is recovered.

The term “equal percentage characteristic” as used herein should beunderstood to mean an inherent flow characteristic which, for equalincrements of rated travel, will ideally give equal percentage changesof the existing flow coefficient (Cv).

The valve characteristic term “inherent” as used herein should beunderstood to mean the relationship between the flow coefficient (Cv)and the closure member travel as it is moved from the closed position torated travel with constant pressure drop across the valve.

The valve characteristic term “linear” as used herein should beunderstood to mean an inherent flow characteristic that can berepresented by a straight line on a rectangular plot of flow coefficient(Cv) versus rated travel. Therefore, equal increments of travel provideequal increments of flow coefficient (Cv).

The valve characteristic term “quick opening” as used herein should beunderstood to mean an inherent flow characteristic in which a maximumflow coefficient is achieved with minimal closure member travel.

The term “cam” as used herein should be understood to mean a componentin a valve positioner used to relate the closure member position to thecontrol signal.

The term “trim” as used herein should be understood to mean a controlvalve trim that provides predefined flow characteristics.

The term “closure member” as used herein should be understood to meanthe movable part of the valve that is positioned in the flow path tomodify the rate of flow through the valve. A closure memberconfigurations referred to as a “plug” is characterized as a closuremember with contoured surface, such as the “vee plug,” to providevarious flow characteristics. A closure member configuration referred toas “cylindrical” is a cylindrical closure member with a flow passagethrough it (or a partial cylinder).

The term “eccentric” as used herein should be understood to mean aclosure member face is not concentric with the stem centerline and movesinto seat when closing.

The term “eccentric spherical disk” as used herein should be understoodto mean a disk is spherical segment, not concentric with the disk stem.

The term “linear” as used herein should be understood to mean a closuremember that moves in a line perpendicular to the seating plane.

The term “rotary” as used herein should be understood to mean a closuremember which is rotated into or away from a seat to modulate flow.

The term “coefficient of flow” or the constant “Cv” as used hereinshould be understood to mean the related to the geometry of a valve, fora given valve travel, that can be used to predict flow rate.

The term “control valve” as used herein should be understood to mean avalve which controls the flow rate or flow direction in a fluid system.The final control element, through which a fluid passes, that adjuststhe flow passage as directed by a signal from a controller to modify theflow rate.

The term “dual sealing valve” as used herein should be understood tomean a valve that uses a resilient seating material for the primary sealand a metal-to-metal seat for a secondary seal.

The term “end connection” as used herein should be understood to meanthe configuration provided to make a joint with the pipe. Endconnections may be “flanged” in which a valve body has end connectionsincorporating flanges that mate with corresponding flanges on thepiping. An end connection may be “split clamp” in which a valve endconnections of various proprietary designs using split damps to applygasket or mating surface loading. An end connection may be “threaded” inwhich the valve end connections incorporating threads, either male orfemale. The valve end connections may be “welded” in which valve endconnections which have been prepared for welding to the line pipe orother fittings. These bay be of butt weld (BW) or socket weld (SW)types.

The term “erosion resistant trim” as used herein should be understood tomean a valve trim that has been designed with special surface materialsor geometry to resist the erosive effects of the controlled fluid flow.

The term “extension bonnet” as used herein should be understood to meana bonnet with a packing box that is extended above the bonnet joint ofthe valve body so as to maintain the temperature of the packing above orbelow the temperature of the process fluid. The length of the extensionbonnet is dependent upon the difference between the fluid temperatureand the packing design temperature limit as well as upon the valve bodydesign.

The term “face to face dimension” as used herein should be understood tomean the dimension from the face of the inlet opening to the face of theoutlet opening of a valve or fitting.

The term “flange facing” as used herein should be understood to mean thefinish on the end connection that mates with gasket surfaces.

The term “failure mode” as used herein should be understood to mean theposition to which the valve closure member moves when the actuatingenergy source fails. The term “fail-closed” as used herein should beunderstood to mean a condition wherein the valve closure member moves toa closed position when the actuating energy source fails. The term“fail-in place” as used herein should be understood to mean a conditionwherein the valve closure member stays in its last position when theactuating energy source fails. The term “fail-open” as used hereinshould be understood to mean a condition wherein the valve closuremember moves to an open position when the actuating energy source fails.

The term “fail-safe” as used herein should be understood to mean acharacteristic of a particular valve and its actuator, which upon lossof actuating energy supply will cause a valve closure member to fullyclose; fully open or remain in fixed last position. Failsafe action mayinvolve the use of auxiliary controls connected to the actuator.

The term “flangeless control valve” as used herein should be understoodto mean a valve without integral line flanges, which is installed bybolting between companion flanges, with a set of bolts, or studs,generally extending through the companion flanges.

The term “guides” or “closure guides” as used herein should beunderstood to mean the means by which the closure is aligned with theseat and held stable throughout its travel. The guide is held rigidly inthe body, bonnet, and/or bottom plate.

The term “hand jack” as used herein should be understood to mean amanual override device, using a lever, to stroke a valve or to limit itstravel. The term “handwheel” as used herein should be understood to meanone such hand jack in which a mechanical manual override device, using arotary wheel, is used to stroke a valve or to limit its travel.

The term “hard facing” as used herein should be understood to mean amaterial applied to valve internals to resist fluid erosion and/or toreduce the chance of galling between moving parts, particularly at hightemperatures.

The term “hard plating: as used herein should be understood to mean athin metal deposit, sometimes electroplated, and used to induce surfacehardening. Hard plating is many orders of magnitude thinner than hardfacing.

The term “hysteresis” as used herein should be understood to mean themaximum difference in output value for any single input value during acalibration cycle, excluding errors due to dead band.

The term “Integral seat” as used herein should be understood to mean aflow control orifice and seat that is an integral part of the body orcage.

The term “jacketed valve” as used herein should be understood to mean avalve body cast with a double wall or provided with a double wall bywelding material around the body so as to form a passage for a heatingor cooling medium. Also refers to valves which are enclosed in splitmetal jackets having internal heat passageways or electric heaters. Theterm also referred to as “steam jacketed” or “vacuum jacketed.” In avacuum jacketed valve, a vacuum is created in the space between the bodyand secondary outer wall to reduce the transfer of heat by convectionfrom the atmosphere to the internal process fluid, usually cryogenic.

The term “lantern ring” as used herein should be understood to mean arigid spacer assembled in the packing box with packing normally aboveand below it and designed to allow lubrication of the packing or accessfor a leak-off connection.

The term “lapping-in” as used herein should be understood to mean aprocess of mating contact surfaces by grinding and/or polishing.

The term “leakage” as used herein should be understood to mean aclassification established by ANSI 816.104 to categorize seat leakagetolerances for different sizes of control valve trim. The term “seatleakage” as used herein should be understood to mean the quantity offluid passing through a valve when the valve is in the fully closedposition with pressure differential and temperature as specified.

The term “leak-off gland” as used herein should be understood to mean apacking box with packing above and below the lantern ring so as toprovide a collection point for fluid leaking past the primary seal(lower packing).

The term “lined valve body” as used herein should be understood to meana valve body in which a coating or liner has been applied to internalsurfaces for corrosion/erosion protection or for flow shut off.

The term “slip-in liner” as used herein should be understood to mean anannular shaped liner which makes a slight interference fit with the bodybore and which may be readily forced into position through the body end.It may be plain or reinforced and applies to butterfly valves.

The term “liquid pressure recovery factor” as used herein should beunderstood to mean the ratio (FL) of the valve flow coefficient (Cv)based on the pressure drop at the vena contracta, to the usual valveflow coefficient (Cv) which is based on the overall pressure drop acrossthe valve in non-vaporizing liquid service. These coefficients comparewith the orifice metering coefficients of discharge for vena contractataps and pipe taps, respectively. See ANSI/ISA-S75.01 “Control ValveSizing Equations.”

The term “mechanical limit stop” as used herein should be understood tomean a mechanical device to limit the valve stem travel.

The term “mounting position” as used herein should be understood to meanthe location and orientation of an actuator or auxiliary componentrelative to the control valve. This can apply to the control valveitself relative to the piping.

The term “multiple orifice” as used herein should be understood to meana style of valve trim where the flow passes through a multiple oforifices in parallel or in series.

The term “nominal size” as used herein should be understood to mean anumerical designation of size which is common to all components in apiping system other than components designated by outside diameters orby thread size. It is a convenient round number for reference purposesand is only loosely related to manufacturing dimensions. ISO usesinitials ON as an abbreviation for the term with the letters ON followedby a numerical value designating size. All equipment of the same nominalsize and nominal pressure rating shall have the same mating dimensionsappropriate to the type of end connections.

The term “packing” as used herein should be understood to mean a sealingsystem consisting of deformable material contained in a packing boxwhich usually has an adjustable compression means to obtain or maintainan effective seal. The term “packing box” as used herein should beunderstood to mean the chamber, in the bonnet, surrounding the stem andcontaining packing and other stem sealing parts. The term “packingflange” as used herein should be understood to mean a device thattransfers the deforming mechanical load to the packing follower.

The term “packing follower” as used herein should be understood to meana part which transfers the deforming mechanical load to the packing fromthe packing flange or nut.

The term “packing lubricator assembly” as used herein should beunderstood to mean a device for injection of lubricant/sealer into alubricator packing box.

The term “plug” as used herein should be understood to mean broadly anytype of closure member. The term “plug valve” as used herein should beunderstood to mean a rotary motion valve with a closure member that maybe cylindrical or conical.

The term “port” as used herein should be understood to mean the flowcontrol orifice of a control valve. The term “valve port guiding” asused herein should be understood to mean a closure member with wings ora skirt fitting into the seat ring bore.

The term “positioner” as used herein should be understood to mean aposition controller, which is mechanically connected to a moving part ofa final control element or its actuator, and automatically adjusts itsoutput pressure to the actuator in order to maintain a desired positionthat bears a predetermined relationship to the input signal. Thepositioner can be used to modify the action of the valve (reversingpositioner), extend the stroke/controller. The term “double actingpositioner” as used herein should be understood to mean a positionerwith two outputs, suited to a double acting actuator. The term “singleacting positioner” as used herein should be understood to mean apositioner with one output, suited to a spring opposed actuator.

The term “position switch” as used herein should be understood to mean aposition switch is a pneumatic, hydraulic or electrical device which islinked to the valve stem to detect a single, preset valve stem position.

The term “position transmitter” as used herein should be understood tomean the position transmitter is a device that is mechanically connectedto the valve stem or shaft and generates and transmits a pneumatic orelectrical signal representing the valve position.

The term “post guiding” as used herein should be understood to mean adesign using guide bushing or bushings fitted into the bonnet or body toguide the plug's post.

The term “pressure energized seal” as used herein should be understoodto mean a seal energized by differential pressure.

The term “rangeabillty” as used herein should be understood to mean theinherent ratio of the largest flow coefficient (Cv) to the smallest flowcoefficient (Cv) within which the deviation from the specified inherentflow characteristic does not exceed the stated limits.

The term “rated travel” as used herein should be understood to mean theamount of movement of the valve closure member from the closed positionto the rated full open position.

The term “seat” as used herein should be understood to mean the area ofcontact between the closure component and its mating surface whichestablishes valve shut-off.

The term “seat ring” as used herein should be understood to mean a partof the valve body assembly that provides a seating surface for theclosure member and may provide part of the flow control orifice.

The term “shaft: as used herein should be understood to mean themechanical member used to support a rotary closure member.

The term “spring rate: as used herein should be understood to mean theforce change per unit change in length of a spring.

The term “stem connector” as used herein should be understood to meanthe device which connects the actuator stem to the valve stem.

The term “stem guide” as used herein should be understood to mean aguide bushing closely fitted to the valve stem and aligned with theseat.

The term “three-way valve” as used herein should be understood to mean avalve with three end connections, used for mixing or diverting flow.

The term “throttling” as used herein should be understood to mean theaction of a control valve to regulate fluid flow by varying the positionof the closure member. This service generates a variable pressure drop.

The term “transducer” as used herein should be understood to mean adevice that is actuated by power from one system and supplies power inanother form to a second system.

The term “travel” as used herein should be understood to mean themovement of the closure member from the closed position to anintermediate or rated full open position. The term “travel indicator” asused herein should be understood to mean a pointer and scale used toexternally show the position of the closure member; typically in termsof units of opening percent of travel or degrees of rotation.

The term “trim” as used herein should be understood to mean the internalcomponents of a valve which modulate the flow of the controlled fluid.The term “anti-cavitation trim” as used herein should be understood tomean a combination of control valve trim that by its geometry reducesthe tendency of the controlled liquid to cavitate. The term “anti-noisetrim” as used herein should be understood to mean a combination ofcontrol valve trim that by its geometry reduces the noise generated byfluid flowing through the valve. The term “balanced trim” as used hereinshould be understood to mean a control valve trim designed to minimizethe net static and dynamic fluid flow forces acting on the trim. Theterm “reduced trim” as used herein should be understood to mean acontrol valve trim which has a flow area smaller than the full flow areafor that valve. The term “soft seated trim” as used herein should beunderstood to mean a valve trim with an elastomeric, plastic or otherreadily deformable material used either in the closure component or seatring to provide tight shutoff with minimal actuator forces.

The term “dynamic unbalance” as used herein should be understood to meanthe net force/torque produced on the valve stem/shaft by fluid pressureacting on the closure member and stem/shaft at stated travel and flowingconditions. The term “static Unbalance” as used herein should beunderstood to mean the net force produced on the valve stem by the fluidpressure acting on the closure member and stem with the fluid at restand with stated pressure conditions.

The term “valve” as used herein should be understood to mean a deviceused for the control of fluid flow, consisting of a fluid retainingassembly, one or more ports between end openings and a movable closuremember which opens, restricts or closes the port(s).

The term “ball valve” as used herein should be understood to mean avalve with a rotary motion closure member consisting of a full ball or asegmented ball.

The term “diaphragm type” as used herein should be understood to mean avalve with a flexible linear motion closure member which is moved intothe fluid flow passageway of the body to modify the rate of flow throughthe valve by the actuator.

The term “floating ball valve” as used herein should be understood tomean a valve with a full ball positioned within the valve that contactseither of two seat rings and is free to move toward the seat ringopposite the pressure source when in the closed position to effect tightshutoff.

The term “globe valve” as used herein should be understood to mean avalve with a linear motion closure member, one or more ports and a bodydistinguished by a globular shaped cavity around the port region.

The term “vena contracta” as used herein should be understood to meanthe location in a flow stream where fluid velocity is at its maximum andfluid static pressure and the cross sectional area are at their minimum.In a control valve, the vena contracta normally occurs just downstreamof the actual physical restriction.

The term “yoke” as used herein should be understood to mean thestructure which rigidly connects the actuator power unit to the valve.

1. Detailed Description of the Figures

Referring now FIG. 1 and FIG. 2 a dual mode electropneumatic flowcontrol valve is shown, generally noted as 100, according to thepreferred embodiment of the present invention, in which a singleintegrated valve 100 incorporates a proportional valve component 102 inoperational and physical coordination with a pressure regulator valvecomponent 104. Generally, the flow path of fluid being regulated throughthe valve 100 can be characterized as passing initially through theregulator component 102 whereby pressure is regulated to within amanageable range for operation of a balanced type proportional valvecomponent 102.

Referring now in conjunction with FIG. 2, the dual mode electropneumaticflow control valve 100 can be described in greater detail in which anincoming pneumatic pressure is applied at pressure inlet port 26. Theincoming pressure is in fluid communication with an inner valve 14,which is mechanically attached to an internal regulator 17. As should beunderstood by a person having ordinary skill in the relevant art, inlight of the present teachings, the internal regulator 17 may bepreferably calibrated by adjusting resistance of a mechanically attachedfirst spring 19.

Incoming pressure from the regulator 17 is subsequently allowed to passthrough the inner valve 14 until a desired regulated pressure isobtained in the pressure chamber 28.

The pressure chamber 28 is in fluid communication first with a flowpassageway 27, and then with a valve orifice 23. The valve orifice 23 isobstructed by a valve armature 16. The valve orifice 23, when notobstructed by valve armature 16, is in fluid communication with achamber 22.

The chamber 22 is in fluid communication with a proportional valveorifice 23. When a proportional valve coil 3 is activated by a current,the proportional valve armature 16 is pulled away from the valve orifice23, which creates fluid communication with chamber 22. The proportionalvalve actuation therefore uses said regulated pressure to vary flow ratethrough said valve orifice 23 and out flow passageway 24 and then outletport 25.

2. Operation of the Preferred Embodiment

In operation, the present invention establishes a uniqueelectropneumatic proportional flow control device and method that allowsfor improved valve actuation and an improved turndown ratio in regardsto the electromagnetic response of the device to a supplied controlvoltage. This is achieved using two variable spring devices, one linear,as shown in conjunction with FIG. 4, and one nonlinear, as shown inconjunction with FIG. 3. The linear spring device 12 and nonlinearspring device 11 are each part of the pressure regulator valve component104. Both the linear spring 12 and non-linear spring 11 are eachmagnetically responsive to different magnetic forces.

As shown in conjunction with FIG. 3, the nonlinear spring 11 is a flatcoil spring having a plurality of orbital beams 122. Each orbital beam122 is includes a folded arm 124 that provides a moving fulcrum pointupon movement of orbital spring element. Such a design providesincreased mechanical strength along the last portions of spring travelas compared to the first portions of spring travel.

As shown further in conjunction with FIG. 4, a linear spring 12 isprovided as a flat coil spring in which a preloaded spring tension isapplied in order to provide a predictable preloaded travel at the valveopening. The linear spring 12 improves the valve actuation. Valveactuation is accomplished through precision control over the initial“lift off current”, which is the current required to initiate flowthrough the valve. This overcomes the preloaded spring force which sealsthe inner valve to the valve seat. By using a linear spring, which isresponsive to the relatively lower beginning magnetic pull of the valvecoil, there is less variation in setting the initial preload force ofthe spring.

The non-linear spring 11 is utilized for the relatively higher magneticpull of the valve coil for improved control over the greater magneticforce required for higher flow rates. The non-linear spring forceresistant to the magnetic force is related non-linearly. The use of boththe linear and non-linear springs together results in an increasedturndown-ratio, especially during initial valve control.

The foregoing descriptions of specific embodiments of the presentinvention are presented for purposes of illustration and descriptiononly. They are not intended to be exhaustive or to limit the inventionto the precise forms disclosed and, obviously, many modifications andvariations are possible in light of the above teaching. The embodimentsare chosen and described in order to best explain the principles of theinvention and its practical application, to thereby enable othersskilled in the art to best utilize the invention and the embodimentswith various modifications as are suited to the particular usecontemplated. It is intended that a scope of the invention be defined bythe Claims appended hereto and to their equivalents. Therefore, thescope of the invention is to be limited only by the following claims.

What is claimed is:
 1. An electropneumatic proportional flow control valve comprising: a housing, a proportional valve coil disposed in the housing, a chamber defined in the housing, an armature disposed in the chamber, wherein the armature is positioned on a seat, wherein the armature includes a main body portion and a stem that extends upwardly from the main body portion, wherein the armature is configured to travel a distance from a seated position to a fully open position when the proportional valve coil provides a magnetic pull; a linear spring device having a linear spring force and a first central opening therein; and a non-linear spring device having a non-linear spring force and a second central opening therein, wherein the stem of the armature extends through the first and second central openings, wherein the linear spring device is positioned between the main body portion of the armature and the non-linear spring, wherein between the seated position and the fully open position, the armature moves through a first travel portion and a second travel portion, wherein as the armature moves through the first travel portion the linear spring device applies the linear spring force to the armature, wherein as the armature moves through the second travel portion the non-linear spring device applies the non-linear spring force to the armature, and wherein the non-linear spring force increases as the armature moves through the second travel portion.
 2. The electropneumatic proportional flow control valve of claim 1, wherein said non-linear spring device is utilized for a higher magnetic pull of the proportional valve coil at higher flow rates.
 3. The electropneumatic proportional flow control valve of claim 2, wherein said linear spring and said non-linear spring operate together during a third portion of the distance.
 4. The electropneumatic proportional flow control valve of claim 1 wherein the housing includes an upper housing portion and a lower housing portion, wherein the upper housing portion is separable from the lower housing portion.
 5. The electropneumatic proportional flow control valve of claim 4 further comprising a proportional valve component and a pressure regulator component, wherein the proportional valve component includes the proportional valve coil and the chamber, wherein the proportional valve coil is positioned in the upper housing portion and the chamber is defined in the lower housing portion, wherein the armature is disposed in the lower housing portion, and wherein the stem extends upwardly into the upper housing portion.
 6. The electropneumatic proportional flow control valve of claim 5 wherein the pressure regulator component is contained within the lower housing portion, wherein the pressure regulator component includes an inlet port and an outlet port defined in the lower housing portion, wherein the inlet port is in flow communication with a pressure chamber that includes an internal regulator therein, wherein the internal regulator is movable between a closed position and an open position by a first spring that is positioned at a distal end of the lower housing, wherein the internal regulator is in contact with an internal valve, and wherein when the first spring moves the internal regulator to the open position, the pressure chamber is fluidly communicated with a valve orifice that is associated with the seat.
 7. The electropneumatic proportional flow control valve of claim 6 wherein when the proportional valve coil is energized the armature moves upwardly, thereby fluidly communicating the valve orifice with the chamber and the outlet port.
 8. The electropneumatic proportional flow control valve of claim 1 wherein the magnetic pull of the proportional valve coil is stronger on the armature during the second portion of the distance than during the first portion of the distance.
 9. The electropneumatic proportional flow control valve of claim 1 wherein during at least a portion of the distance the linear spring device and non-linear spring device act concurrently on the armature. 